Photon and spin dependence of the resonance lines shape in the strong coupling regime

TL;DR

This paper investigates the quantum dynamics of a spin ensemble coupled to cavity photons, analyzing how the eigenenergy structure influences spectral features and spin behavior in the strong coupling regime, supported by experimental correlations.

Contribution

It provides a detailed theoretical analysis of the eigenenergy distribution and spectral features in spin-photon systems, connecting these to experimental observations of strong coupling phenomena.

Findings

Transition from vacuum Rabi splitting to single peak spectra with energy level changes

Spin dynamics correspond to cavity ringing and Rabi oscillations in different spectral regions

Dissipation effects alter linewidth and peak separation in the spectra

Abstract

We study the quantum dynamics of a spin ensemble coupled to cavity photons. Recently, related experimental results have been reported, showing the existence of the strong coupling regime in such systems. We study the eigenenergy distribution of the multi-spin system (following the Tavis-Cummings model) which shows a peculiar structure as a function of the number of cavity photons and of spins. We study how this structure causes changes in the spectrum of the admittance in the linear response theory, and also the frequency dependence of the excited quantities in the stationary state under a probing field. In particular, we investigate how the structure of the higher excited energy levels changes the spectrum from a double-peak structure (the so-called vacuum field Rabi splitting) to a single peak structure. We also point out that the spin dynamics in the region of the double-peak structure corresponds to recent experiments using cavity ringing while in region of the single peak structure, it corresponds to the coherent Rabi oscillation in a driving electromagnetic filed. Using a standard Lindblad type mechanism, we study the effect of dissipations on the line width and separation in the computed spectra. In particular, we study the relaxation of the total spin in the general case of a spin ensemble in which the total spin of the system is not specified. The theoretical results are correlated with experimental evidence of the strong coupling regime, achieved with a spin 1/2 ensemble.